The Research On Assembly Sequence Planning And Its Simulation Based On STEP

With the development of Computer Integrated Manufacturing System(CIMS) and Concurrent Engineering(CE), the effect of assembly on the design and manufacture of product is receiving more and more recognition, but the backward present situation of assembly technique is not consistent with its function, it is urgent to develop Computer Aided Assembly Process Planning(CAAPP) in the integrated environment. In the CAAPP, the Assembly Sequence Planning (ASP) is the key problem, which is the prerequisite of Assembly Path Planning and Assembly Process Simulation (APS). This paper detailedly discusses the ASP and APS based on STEP (Standard for the Exchange of Product Model Data).Firstly, object-oriented assembly model based on STEP is established and all information related to assembly is congregated into the database of assembly process, then on the foundation of integrated assembly database, according to the object-oriented idea, many class structures used for ASP and APS are built with C++ language, the data in the assembly process database is read and stored in the relevant class structure. Under computer memory pattern, assembly relationships are automatically recognized according to the geometry information.Assembly model is layered according to the STEP neutral document of assembly and simplified according to the project semantics information. On the basis of layered and simplified assembly model, in view of the complexity and fuzziness of ASP, a new ASP method based on fuzzy appraisal is proposed. The concept of base modulus for part and weight value for assembly relationship is proposed for the first time, the arithmetic of fuzzy appraisal is also proposed. On the basis of modulus and weight value, a new method based on depth-first-search is adopted to create assembly sequence tree with the most inspiration information, the assembly sequence is obtained by searching the assembly tree according to the principle of choosing superior in overall situation.Three-dimensional simulation environment based on OpenGL is established, assembly process is simulated according to planned sequence, Assembly path is specified by man-machine interactive. The quick interference check, based on axis-aligned bounding box, whose result is used for the adjusting of assembly sequence, is made in the simulation.